THE ANTIINFLAMMATORY MECHANISM OF SULFASALAZINE IS RELATED TO ADENOSINE RELEASE AT INFLAMED SITES

The anti-inflammatory mechanism of sulfasalazine is not well understoo d, It has recently been shown that sulfasalazine inhibits 5-aminoimida zole-4-carboxamidoribonucleotide (AICAR) transformylase, an enzyme inv olved in de novo purine biosynthesis, We recently demonstrated that me thotrexate promotes intracellular AICAR accumulation, thereby increasi ng adenosine release and diminishing inflammation, so we tested the hy pothesis that sulfasalazine similarly promotes intracellular AICAR acc umulation, We studied adenosine release and the state of inflammation in in vitro and in vivo models of the inflammatory process, The adhesi on of stimulated neutrophils (FMLP) to endothelial cells preincubated with sulfasalazine was inhibited in a dose-dependent manner, Eliminati on of extracellular adenosine by addition of adenosine deaminase or in hibition of adenosine by the adenosine A(2) receptor antagonist 3,7-di methyl-1-propargy/xanthine (DMPX) completely reversed the anti-inflamm atory effect of sulfasalazine (at concentrations <1 mu M) in this in v itro model, To determine whether this phenomenon was relevant to inhib ition of inflammation in vivo, we studied the effect of sulfasalazine (100 mg/kg/day by gastric gavage for 3 days) on leukocyte accumulation in the murine air pouch model of inflammation, Treatment with sulfasa lazine markedly decreased the number of leukocytes that accumulated in the inflamed (carrageenan, 2 mg/ml) air pouch, Injection of either ad enosine deaminase or DMPX, but not the A, receptor antagonist 8-cyclop entyl-dipropylxanthine, significantly reversed the anti-inflammatory e ffects of sulfasalazine treatment, Sulfasalazine increased the exudate adenosine concentration from 127 +/- 64 nM to 869 +/- 47 nM, Moreover , sulfasalazine treatment promoted a marked increase in splenocyte AIC AR concentration from 35 +/- 6 to 96 +/- 3 pmols/10(6) splenocytes, wh ich is consistent with the in vitro observation that sulfasalazine inh ibits AICAR transformylase, These results indicate that sulfasalazine, like methotrexate, enhances adenosine release at an inflamed site and that adenosine diminishes inflammation via occupancy of A(2) receptor s on inflammatory cells, Our studies provide evidence that sulfasalazi ne and methotrexate may be described as a newly recognized family of a nti-inflammatory agents that share the property of using adenosine as an antagonist of inflammation.